1. Field of the Invention
The present invention pertains to pressure-operated valves. More particularly, the present invention relates to continuous operation, pressure-regulated valves, wherein such a valve may be opened to permit more or less fluid flow therethrough based, at least in part, on the amount of pressure applied to the valve generally from the downstream side. The present invention finds particular application to gas lift valves for use in gas lift operations in the production of fluid from wells, for example.
2. Discussion of Prior Art
Gas lift valves are known for use in gas lift operations in the production of fluid from wells, such as oil wells. Such valves may be positioned at selected depths in the well, and serve to control the flow of gas from a control line or casing surrounding the tubing string through which fluid is to be produced, and the interior of the tubing string. Infusion of such gas into the oil, for example, reduces the density of the oil and allows the oil at the level of the gas influx to be elevated by oil of greater density below. As the density of the oil decreases, and the oil becomes lighter, the oil tends to apply less pressure on the gas lift valve, and on higher gas lift valves along the well, which might be closed.
In general, such a gas lift valve may be pressure-operated so that the opening and closing of the valve may be controlled. The gas under pressure to be introduced into the liquid also provides a control pressure which, when applied to the valve, may urge the valve open against forces tending to maintain the valve closed. Such closing forces may be applied by a spring, for example, in addition to a charging fluid, such as nitrogen gas, for example. The charging fluid is applied to the valve prior to its introduction into the well, and sets a reference pressure against which forces tending to open the valve must work. With the valve in place and its outlet exposed to the fluid in the production tubing, the production tubing pressure also urges the valve to open. However, the ultimate control of the valve lies to a substantial extent with the pressure of the PG,3 control gas. Thus, to close the valve or to adjust the amount the valve is open for communication of gas therethrough, the pressure of the control gas is adjusted by appropriate operations at the surface.
It is advantageous, however, to provide a gas lift valve whose configuration may be controlled by the pressure in the tubing at the level of the valve, without the necessity of monitoring that pressure from the surface, for example. Such a valve may be referred to as a continuous lift, or continuous operation, valve. To achieve such continuous operation, the valve may be constructed to provide the input control gas with a pressure drop other than at the operable opening of the valve, that is, between the valve element and its seat. This may be achieved by use of an orifice arrangement, whereby the control gas input to the valve must flow through a constriction and thus undergo a pressure drop before being introduced into the tubing string through the valve opening. Then, the tubing string pressure may exert the predominant influence to control the configuration of the valve, that is, to determine whether and to what extent the valve is open. When the fluid pressure in the tubing string at the level of the valve decreases, reflecting a decrease in the density of the liquid at that level, the valve may be closed partly or completely, under the influence of the gas charge and the spring device for example, and the liquid elevated by the greater density liquid below without influx, or with limited influx, of control gas into the liquid. When the pressure in the tubing string at the valve increases, reflecting liquid of greater density at that level, the valve is opened, or opened to a greater extent, due to the increase in fluid pressure urging the valve opened, to permit an influx, or greater influx, of control gas into the tubing string to lower the density of the liquid for production.
It is further advantageous to provide such a continuous lift valve with a readily replaceable orifice component, since such a constriction may be particularly exposed to damage through erosion due to particles that may be carried by the inflowing control gas. It is also advantageous to provide such a gas lift valve with a readily replaceable component which bears the brunt of any such erosion caused by particles carried by the gas as the control gas is initially inlet into the interior of the valve itself. The present invention provides such advantages.